Actually, I could believe it (although I have no info). As I understand it, there's only one road in/out of NO. It is easy to imagine police deciding to clear the roads of foot traffic so the convoys could go back and forth. It would be infuriating to be trapped that way, but I could easily see how it might happen.
Yeah, I thought of that as soon as I posted. But Shep also said people are LOCKED INSIDE the convention center. There's no way that's true.